As is well known in the art, a switching power supply device means a power converter for converting a DC voltage (input voltage) having a particular voltage level into a DC voltage (output voltage) having another voltage level. The switching power supply device is also called a DC-DC converter or a switching regulator. In the switching power supply device, a transistor is used as a switch and is switched to convert the input voltage into an AC voltage. Then, the voltage is stepped up or stepped down by an inductance element, such as a transformer or an inductor, and thereafter rectified to be converted into the output voltage.
As a switching power supply device of the type, there is a device using a first power supply circuit having a small output and a second power supply circuit having a large output. The first power supply circuit is used to supply an electric power to a control circuit, as a load, which operates in response to a command signal as an electric wave (for example, an infrared ray) from a remote controller. The second power supply circuit is used to supply an electric power to a device body (set circuit) as a load. The conventional switching power supply device is continuously kept in an operating state once it is started. In other words, the first power supply circuit and the second power supply circuit are continuously kept in an operating state regardless of a state of the load.
Various prior art techniques related to the present invention are known. For example, Patent Document 1 discloses a switching power supply device in which an AC power supply input is supplied to a rectifier through a filtering inductance element and an output from the rectifier is subjected to switching control. In the switching power supply device, an additional winding is provided for the above-mentioned filtering inductance element and, by an output from the additional winding, a starting power is supplied to a circuit section for carrying out the switching control mentioned above.
Further, Patent Document 2 discloses an improved dual power supply circuit for generating two kinds of power supply voltages. The power supply circuit disclosed in Patent Document 2 is used in a device requiring two kinds of power supply voltages, i.e., a high-level power supply voltage and a low-level power supply voltage. The power supply circuit is used when such two kinds of power supply voltages are supplied by one power supply circuit. The power supply circuit comprises a first voltage generating section for generating a first output voltage (high-level power supply voltage) and a second voltage generating section for generating a second output voltage (low-level power supply voltage). The first voltage generating section is provided with a first control section, while the second voltage generating section is provided with a second control section. Between a power supply voltage input terminal of the second control section and a power supply voltage input terminal of the first control section, a switching circuit is provided which is turned on when a potential of the power supply voltage input terminal of the second control section is increased over a predetermined potential. This switching circuit supplies a power supply voltage to the first control section after the second control section is completely started. Therefore, the first voltage generating section is started only after the second voltage generating section is started.
Furthermore, Patent Document 3 discloses a switching power supply comprising a power supply for starting a PWM circuit and suppressing power consumption with a simple structure. This switching power supply disclosed in Patent Document 3 comprises a first converter, a second converter, and the PWM circuit. The PWM circuit starts, before starting the first converter, the second converter for supplying an electric power to the PWM circuit upon start-up of the switching power supply.
Furthermore, Patent Document 4 discloses a technique for supplying a storage power of a single-systematic battery to a circuit, such as a central processing unit of a computer, and to a start-up circuit, while suppressing an expansion of a scale of a power supply device. The power supply device disclosed in Patent Document 4 is a power supply device for use in a computer and comprises two transformers including a main transformer used in a feeding system for feeding an electric power to a circuit, such as a central processing unit, and a backup transformer used in a feeding system for feeding an electric power to the start-up circuit. A charged voltage of an input capacitor is charged into an output capacitor through the backup transformer. A charged voltage of this output capacitor is outputted to the start-up circuit. An electric power produced by the backup transformer is supplied to an output voltage control circuit. If a start-up switch is operated in the above-mentioned state, the start-up circuit produces a start-up signal. Responsive to the start-up signal, the output control circuit starts an operation. Consequently, the charged voltage of the input capacitor is supplied to the central processing unit through the main transformer.
Patent Document 1: Japanese Unexamined Utility Model Application Publication (JP-U) No. S57-151627
Patent Document 2: Japanese Patent Publication (JP-B) No. 3244424
Patent Document 3: Japanese Unexamined Patent Application Publication (J P-A) No. 2002-199723
Patent Document 4: Japanese Unexamined Patent Application Publication (JP-A) No. 2005-110346